FOLLOW UP
I never got answer from Fantastic site about motor lubrication, but I run the fan for about 1 hr few days ago, disregarding some noise and the motor is dead today.
I emailed Fantastic via their site again and got response from DometicUSA that when motors can't be lubricated, I would have to pay $30 for new one.
Since I don't plan to go home for another month, I have to wait for the repair.
BTW I emailed torklift if their tie-downs can be used reversed as their system is letting my camper to slide back. No response.